1. Field of the Invention
This invention relates to an infrared sensor of a Schottky barrier diode type. This invention also relates to an infrared camera including such an infrared sensor.
2. Description of the Prior Art
Infrared sensors are basically of a pyroelectric type or a quantum type. Some quantum-type infrared sensors use the photoconductivity of an intrinsic semiconductor, such as HgCdTe, which has a band gap of 0.1-0.3 eV. Other quantum-type infrared sensors use the photoelectric effect of a Schottky barrier diode, such as Pt/p-type Si, which has a small barrier height.
Advanced visible light image sensors already use charge-coupled devices (CCD) of Si. It has been desired to combine an infrared sensor and CCD to realize a CCD infrared image sensor.
Pyroelectric-type infrared sensors have slow response speeds so that they are unsuited for infrared image sensors.
Intrinsic semiconductors such as HgCdTe have high sensitivities and are also excellent in the flexibility of sensed wavelengths due to an easy change of their band gaps. However, it is generally difficult to combine such a narrow band gap intrinsic semiconductor and Si-CCD to form a CCD image sensor.
Infrared sensors using Schottky barriers of Pt/p-type Si or PtSi/p-type Si are most excellent in the characteristic of matching to CCD. FIG. 3 shows an energy band diagram of a PtSi-p-type Si Schottky barrier diode. The height of a barrier of this diode is about 0.23 eV, and the barrier height is determined by the substance. Accordingly, the photoelectic sensitivity of such an infrared sensor becomes inadequate at infrared light wavelengths longer than about 5 micrometers. In other words, the longer limit of sensible wavelengths is about 5 micrometers.
N. Yutani et al., Technical Digest of Int. Electron Device Meeting, 1987, pages 124-127, report that when Pt was replaced by Ir in PtSi/p-type Si, the barrier height decreased to about 0.17 eV and, as shown in FIG. 5, the longer limit of sensible wavelengths was about 7 micrometers. However, the longer limit of sensible wavelengths is determined by the substance, and it is generally difficult to further lengthen the longer limit.